Projection optical system and projector apparatus

A projector system comprising:

• a projection optical system that projects from a first image plane on a reducing side to a second image plane on an enlargement side;
• and
• a focusing mechanism that carries out focusing of the projection optical system,
• wherein the projection optical system includes:
• a first refractive optical system that forms a first intermediate image on the enlargement side using light incident from the reducing side;
• a second refractive optical system that forms the first image on the reducing side into a second intermediate image on the enlargement side;
• and
• a first reflective optical system including a first reflective surface with positive refractive power that is positioned on the enlargement side of the second intermediate image, and
• the focusing mechanism includes a mechanism that moves at least one lens included in the second refractive optical system.

A method of carrying out focusing of a projection optical system that projects from a first image plane on a reducing side to a second image plane on an enlargement side,

• wherein the projection optical system includes:
• a first refractive optical system that forms a first intermediate image on the enlargement side using light incident from the reducing side;
• a second refractive optical system that forms the first image on the reducing side into a second intermediate image on the enlargement side;
• and
• a first reflective optical system including a first reflective surface with positive refractive power that is positioned on the enlargement side of the second intermediate image, and
• the method comprises moving at least one lens included in the second refractive optical system.